A known four-wheel-drive vehicle uses a driveline including an engine and a power transmission gear unit which are arranged in series in a fore-and-aft direction of the vehicle. The driving power delivered from the engine is split by means of a power transfer mechanism into two component powers one of which is transmitted through a front final reduction gear unit to the wheel axles for the front road wheels and the other of which is transmitted through a rear final reduction gear unit to the wheel axles for the rear road wheels.
Such a series arrangement of the engine and the power transmission gear unit requires an elongated vehicle chassis and, for this reason, results in deterioration in the stability of steering due to extended overhangs of the vehicle body. Furthermore, the transmission gear unit in the series engine and transmission arrangement occupies a portion of the spaces which could otherwise be utilized as the passenger and baggage spaces, thereby encumbering the availablity of the passenger and baggage spaces of the vehicle.
On the other hand, there is a recent trend to use a front-engine front-wheel-drive system with the engine positioned to have its output shaft in a lateral direction of a vehicle. Such a drive system for a wheeled vehicle is advantageous for improving the stability of steering and unencumbering the space availability of the vehicle. A problem has, however, been encountered in a vehicle driving system of this nature in that the power train including the power transmission gear unit and the front final reduction gear unit of the driving system can not be utilized without modification as the power train in a four-wheel-drive system with an engine positioned to have its output shaft in a lateral direction of the vehicle. The power train for the driving system for a four-wheel-driven vehicle must have therefore be designed and engineered independently of the power train for a front-engine front-wheel-drive system. This requires an additional cost for the designing and engineering of a four-wheel-drive system with an engine positioned to have its output shaft in a lateral direction of the vehicle.
The present invention therefore contemplates provision of a four-wheel-drive system which can be realized by using, without any important modification, the power train of a conventional front-engine front-wheel-drive system with a lateral engine axis.